The practice of using a hydrocyclone to concentrate and separate coarser-sized particles in a particle-laden aqueous suspension has been practiced for over 100 years; however, the duty of industrial hydrocyclones has been significantly expanded over time. Today, particularly in mineral processing applications, high feed rates of solids and the abrasive nature of these particles requires that hydrocyclones be refined and improved to achieve higher capacities, greater solids recovery, and longer service life.
An important aspect of hydrocyclone operational kinetics which affects service life is the fact that rotating flow inside an operating hydrocyclone obeys the laws of free-vortex rotation. In other words, the rotating velocities (tangential velocities) within an industrial hydrocyclone increase as the radius of the hydrocyclone decreases. Mathematically, this condition of “free vortex” is expressed by the equation: “VR=constant”, wherein “V” equals slurry velocity, and “R” equals the radius of the hydrocyclone at a given point. Thus, as slurry rotates and descends toward the bottom of a hydrocyclone, it encounters decreasing radius and increasing velocity.
To satisfy the free-vortex equation, slurry must accelerate tangentially in order to maintain a constant result. For example, if slurry enters a 24 inch diameter hydrocyclone fitted with a 4 inch diameter apex orifice with a linear velocity of 25 feet per second, then slurry descending towards the bottom of the hydrocyclone must accelerate to approximately 150 feet per second or increase its tangential velocity approximately 6 times as it encounters a decreasing radius. Since slurry typically contains abrasive particles which can erode interior portions of a hydrocyclone, increased wear is especially prevalent in areas with smaller inner diameters.
To date, hydrocyclone designers have used various approaches including utilizing internal liners constructed of abrasion-resistant materials. In many instances, such an approach requires a multiple-piece hydrocyclone body. FLSmidth Krebs pioneered this concept of “componentized hydrocyclone design” 50 years ago. The concept utilizes multiple sections of wear-resistant liners held together in respective steel-housings. Typically, the liners were comprised of a flexible elastomeric material, and therefore, problems accompanying the sealing of joints between each liner section did not exist.
However, in the mid 1970's, when “componentized” cyclones were being used in coal processing, elastomeric liners had a short service life because of the abrasiveness of coal particles. Shortly thereafter, FLSmidth Krebs pioneered the use of abrasion-resistant refractory ceramic liners, which, although providing a more abrasion-resistant hydrocyclone, form slight gaps therebetween due to the non-resilient nature of ceramic material. It was discovered that, unlike elastomeric liners, the gaps at each joint between the rigid ceramic liners permitted some exiting of the rotating slurry suspension within the hydrocyclone, thereby causing premature wear of less abrasion-resistant exterior steel housings.
Since hydrocyclones can be comprised of as many as eight or more sections—with each section having one or more joints, chances are significant that at least one liner joint may succumb to slurry penetration and erosion due to the significant amount of kinetic energy in the rotating slurry.
Through the years, various attempts were made to address slurry erosion in the gaps between ceramic liners. The challenge is that ceramic liners are typically formed by slip casting or isostatic pressing while in a “green” (pre-fired) state, meaning liners need to be sized dimensionally about 15% to 17% larger than the desired final product size (post-firing), depending on material composition. These significant shrinkage rates attributable to kiln-firing lead to non-uniformities which make it extremely difficult to close tight joint gap tolerances between ceramic liners—particularly with oddly sized or shaped liners. Moreover, tightening of tolerances for the casting, pressing, and firing steps would lead to higher manufacturing costs and a non-competitive design in the marketplace.
More recent attempts have incorporated the concept of a labyrinth seal or a half lap joint type arrangement built-in to each end of the ceramic liners. An example of such a design can be seen in International Patent Application Publication WO10085331. However, independent tests suggest that interfitted ceramic liners incorporating such mechanical interlocks are extremely vulnerable to damage, since ceramic margins generally extend past the respective casing flange. Moreover, such interfaces introduce a level of stress concentration. Thus, the reliance on traditional labyrinth seals creates a vulnerable ceramic part with a poor resistance to impact. Additionally, higher density abrasive particles have a tendency to orbit in middle and lower sections of a hydrocyclone, further increasing the chance of lap joint failure from orbiting tramp material.
Conventional seals and gaskets commonly used in hydrocyclones are typically made of a solid elastomeric compound such as a urethane or neoprene. The problem with these conventional sealing devices is that they fail to hold up to demanding environments, particularly environments where the sealing devices are subjected to abrasive slurries at high velocities or pressures. Moreover, traditional mechanical interfaces which incorporate seals and gaskets fail to effectively prevent casing blowout as described above. The aforementioned drawbacks are also prevalent in slurry pumps and upper regions of a hydrocyclone, where abrasive slurries under high pressures and/or velocities may escape between components over time. For example, other high wear areas include areas adjacent the vortex finder in a hydrocyclone and areas in slurry pumps adjacent dry glands seals, pump casings, back plates, and hubs.
For example, in a typical hydrocyclone having one or more bolted-together cone sections, a plurality of modular ceramic liner sections protect the inner surfaces of casings which define the outer hydrocyclone housing. Small axial spaces typically exist between the respective mating surfaces of the ceramic liner sections. Slurry passing through these small axial spaces may have large radial velocities and kinetic energy, and can quickly erode both the mating surfaces of the ceramic liners and adjacent portions of the surrounding casings—including flanged connections and external connectors. Such erosion can lead to spewing, leaks, premature maintenance, and other problems with the hydrocyclone. Since abrasive wear from a particle-laden suspension typically increases at approximately the cube of velocity, it is extremely desirable to slow the velocity of slurry in areas of a hydrocyclone which are not protected with wear surfaces.